1. Technical Field
The present invention relates to a method of manufacturing a semiconductor device, and specifically to a method of manufacturing a semiconductor device including a step of forming a silicide film.
2. Related Art
As high integration of semiconductor elements proceeds, it is required that the gate dimensions of a transistor or the interconnect width thereof is miniaturized, and the resistance of gate and source/drain regions decreases for high-speed operation of the transistor. As a technique for solving such a requirement, a salicide process is used in which the resistance of the gate and source/drain regions made of polysilicon is reduced by forming a low-resistance silicide compound of a metal and silicon in a self-aligned manner.
In the salicide process, metals such as Ni, Co, and Ti are formed on a wafer in which the gate and source/drain regions made of polysilicon are formed, and heat treatment is applied thereto. Thereby, the metal is diffused into silicon, or silicon is diffused into the metal, and a silicide film is formed by reacting them with each other. On the other hand, unreacted metal deposited on an element isolation insulating film and a sidewall is selectively removed using a chemical such as a sulfuric hydrogen peroxide mixture or nitrohydrochloric acid after heat treatment. Thereby, the silicide film is selectively formed in the gate and source/drain regions.
Among materials included in the silicide film, nickel silicide which is a compound of nickel and silicon is attracting attention due to an advantage such as stable resistance of the minute gate and source/drain region.
Japanese Unexamined Patent Publication No. 2009-111214 discloses a technique for forming the silicide film in the gate and source/drain regions. Procedures disclosed in the above document will be described with reference to FIGS. 8A, 8B, 8C, 9A and 9B.
First, a semiconductor element is created by forming, on a silicon substrate 1, a shallow trench isolation (STI) 2 used as an element isolation insulating film, a gate electrode 3, a sidewall 4, a gate insulating film 5, an extension region 6, and a source/drain region 7 (FIG. 8A). Next, a metal film 8 such as a Ni—Pt alloy film is formed on the entire surface of the silicon substrate 1 (FIG. 8B). Thereafter, annealing is performed at a temperature of 200 to 350° C., for 30 to 120 seconds under an N2 atmosphere, by lamp annealing and the like, and a silicide film 9 of Ni2Si is formed (FIG. 8C). Subsequently, the unreacted metal film 8 is selectively removed using a sulfuric hydrogen peroxide mixture (FIG. 9A). Next, annealing is performed at a temperature between a temperature higher than 350° C. and a temperature of 600° C., for 30 to 120 seconds, under the N2 atmosphere, by lamp annealing and the like, and the silicide film 9 is formed as a silicide film 11 of NiSi (FIG. 9B).
In addition, Japanese Unexamined Patent Publication No. 2010-28084 discloses procedures for forming the silicide film through the following procedures.
1) Similarly to a general salicide technique, a source/drain diffusion layer made of Si, SiGe, SiC or the like is formed, and Pt-containing Ni is formed on the entire surface of the wafer.
2) Si or SiGe of the source/drain diffusion layer is silicified by performing a first heat treatment, and a Ni silicide film is formed.
3) An unreacted Ni film located on an element isolation insulating film and the like is oxidized by heat treatment of an oxidizing atmosphere, and a Ni oxide film is formed.
4) The composition of the Ni silicide film is set to be Si-rich by performing a second heat treatment having a higher temperature than that of the first heat treatment.
5) The Ni oxide film and Pt are removed using nitrohydrochloric acid.
In a technique disclosed in the above document, the nitrohydrochloric acid is used as a chemical for removing the metal film. Therefore, after the first heat treatment, first, the silicide film is formed as NiSi having a high oxidation resistance to the nitrohydrochloric acid by the high-temperature second heat treatment. Next, the unreacted metal film is removed using the nitrohydrochloric acid. For this reason, the high-temperature second heat treatment is performed in a state where the unreacted metal film remains on the element isolation insulating film. Consequently, in order to prevent the metal film located on the element isolation insulating film from flowing into the source/drain region by migration in the high-temperature second heat treatment, after the first heat treatment and before the high-temperature second heat treatment, the unreacted metal film located on the element isolation insulating film and the like is oxidized by heat treatment of an oxidizing atmosphere, and processing for forming an oxide film is performed.
Herein, though the first heat treatment is carried out in a nitrogen atmosphere, for example, with a temperature of 300° C., it is disclosed that the first heat treatment may be performed at an oxygen concentration of equal to or less than 1%. In addition, it is disclosed that the heat treatment of the oxidizing atmosphere is performed at a temperature of 300° C. or so, and the second heat treatment is performed at a high temperature of equal to or more than 400° C.
However, in the past, for example, in the method disclosed in Japanese Unexamined Patent Publication No. 2009-111214, there has been a problem that a Si oxide 12 (see FIGS. 9A and 9B) is locally formed on the surface of the silicide film. When such an oxide 12 is formed, variation of sheet resistance of the silicide film 11 increases, and poor electrical conduction of a contact occurs.
Such an oxide 12 is considered to be formed as followed. First, since silicide reaction by initial annealing is insufficient, the silicide film richer in Ni (richer in metal) than Ni2Si is locally formed at the surface side of the silicide film. Next, when the unreacted metal film 8 is selectively removed by using a sulfuric hydrogen peroxide mixture, it is considered that Ni is eluted from the Ni-rich silicide film and remaining Si reacts with oxygen, so that the oxide 12 is formed.
In addition, especially, when thinning of the silicide film proceeds, there also occurs a problem that abnormal growths 13 (see FIG. 9B) is easily generated in the direction of the interface of the silicide film 9 with an STI 2 or the direction of the interface thereof with the sidewall 4, and an increase in a junction leakage current or uniformity of the sheet resistance is deteriorated. A cause for generating such abnormal growth 13 includes a fact that since Ni located on the STI 2 or the sidewall 4 flows and diffuses into silicon during the initial annealing, the thickness of the silicide film easily increases. Therefore, measures for preventing Ni located on the insulating film from flowing into silicon are also required.
In the technique disclosed in Japanese Unexamined Patent Publication No. 2010-28084, after the first heat treatment (initial annealing), the unreacted metal film located on the element isolation insulating film and the like is oxidized by the heat treatment of the oxidizing atmosphere, and processing for forming the oxide film is performed. However, in this method, the formation of the oxide 12 or the generation of the abnormal growth 13, as mentioned above, cannot be prevented. In this method, similarly to the technique disclosed in Japanese Unexamined Patent Publication No. 2009-111214, since Ni located on the element isolation insulating film or the sidewall flows and diffuses into silicon during the first heat treatment, the generation of the abnormal growth 13 cannot be prevented.